Process for producing aromatics from a heavy hydrocarbon feed

ABSTRACT

The present invention relates to a process for producing monoaromatic hydrocarbons from a hydrocarbon feed comprising polyaromatics, the process comprising contacting said feed in the presence of hydrogen with a M/zeolite catalyst under hydrocracking process conditions.

The present invention relates to a process for producing monoaromatichydrocarbons from a hydrocarbon feed comprising polyaromatics, theprocess comprising contacting said feed in the presence of hydrogen witha M/zeolite catalyst under hydrocracking process conditions.

Processes for producing monoaromatic hydrocarbons described in Table 4from heavy hydrocarbon feeds have been previously described. Forinstance, US 2007/0062848 describes a process for hydrocracking a feedcomprising not less than 20 weight % of one or more aromatic compoundscontaining at least two fused aromatic rings to produce a product streamcomprising C2-4 alkanes and BTX comprising an aromatic hydrogenationstep and a separate ring cleavage step.

Ma et al. (2007) Catal Letters 116, 149-154 describe the coupledhydrogenation and ring opening of tetralin on potassium modifiedPt/zeolite Y catalysts. The process of Ma et al. is characterized inthat the BTX yield is relatively low. Ma et al. (2007) shows that theextent of successive cracking reactions can be reduced by introducingpotassium into a Pt/zeolite Y catalyst. As a result thereof, however,the process of Ma et al. (2007) has a relatively high selectivity fornon-aromatic C5-C9 hydrocarbons.

It was an object of the present invention to provide an improved processwhich allows the selective conversion of a heavy hydrocarbon feedstockcomprising polyaromatics to monoaromatic hydrocarbons and which has alow selectivity towards unwanted side-products such as methane and/orlower paraffinic hydrocarbons such as LPG and non-aromatic C5-C9hydrocarbons.

The solution to the above problem is achieved by providing theembodiments as described herein below and as characterized in theclaims. Accordingly, the present invention provides a process forproducing monoaromatic hydrocarbons from a hydrocarbon feed comprisingpolyaromatics, the process comprising contacting the feed in thepresence of hydrogen with a M/zeolite catalyst at a pressure ofambient-65 bara, a temperature of 350-500° C., a WHSV of 0.1-10 h⁻¹ anda H₂/HC ratio of 1-20,

wherein said M/zeolite catalyst comprises:

0.05-2.5 wt-% of element M, wherein said element M is one or moreelements selected from Group 10 of the Periodic Table of Elements; and

an aluminosilicate zeolite having a pore size of 6-8 Å and a SiO₂/Al₂O₃ratio of 50-120.

In the context of the present invention, it was surprisingly found thatby specifically selecting the M/zeolite catalyst of the presentinvention and selecting a pressure of ambient-65 bara, a temperature of350-500° C., a WHSV of 0.1-10 h⁻¹ and a H₂/HC ratio of 1-20 as processconditions, a heavy hydrocarbon feed comprising polyaromatic hydrocarboncompounds can be more efficiently converted to monoaromatichydrocarbons. Particularly, the production of unwanted side productssuch as methane and/or C5-C9 hydrocarbons can be reduced by selectingthe process conditions as defined herein in combination with thecatalyst of the present invention over a catalyst and process conditionsas described in the prior art, such as Ma et al, which for instanceinvolves a process temperature of 100-300° C.

The term “aromatic hydrocarbons” or “aromatics” is very well known inthe art. Accordingly, the term “aromatic hydrocarbon” relates tocyclically conjugated hydrocarbon with a stability (due todelocalization) that is significantly greater than that of ahypothetical localized structure (e.g. Kekulé structure). The mostcommon method for determining aromaticity of a given hydrocarbon is theobservation of diatropicity in the 1H NMR spectrum, for example thepresence of chemical shifts in the range of from 7.2 to 7.3 ppm forbenzene ring protons. As used herein, the term “polyaromatics” or“polyaromatic hydrocarbons” relates to hydrocarbons having more than onearomatic ring. As used herein, the term “monoaromatic hydrocarbons” or“monoaromatics” relates to a mixture of aromatic hydrocarbons havingonly one aromatic ring.

The term “BTX” as used herein relates to a mixture of benzene, tolueneand xylenes. Preferably, the product produced in the process of thepresent invention comprises further useful aromatic hydrocarbons such asethylbenzene. Accordingly, the present invention preferably provides aprocess for producing a mixture of benzene, toluene xylenes andethylbenzene (“BTXE”). The product as produced may be a physical mixtureof the different aromatic hydrocarbons or may be directly subjected tofurther separation, e.g. by distillation, to provide different purifiedproduct streams. Such purified product stream may include a benzeneproduct stream, a toluene product stream, a xylene product stream and/oran ethylbenzene product stream.

As used herein, the term “C# hydrocarbons”, or “C#”, wherein “#” is apositive integer, is meant to describe all hydrocarbons having # carbonatoms. Moreover, the term “C#+ hydrocarbons” is meant to describe allhydrocarbon molecules having # or more carbon atoms. Accordingly, theterm “C9+ hydrocarbons” is meant to describe a mixture of hydrocarbonshaving 9 or more carbon atoms. The term “C9+ alkanes” accordinglyrelates to alkanes having 9 or more carbon atoms.

The term “LPG” as used herein refers to the well-established acronym forthe term “liquefied petroleum gas”. LPG generally consists of a blend ofC2-C4 hydrocarbons i.e. a mixture of C2, C3, and C4 hydrocarbons.

Accordingly, the process of the present invention involves contacting ahydrocarbon feed in the presence of hydrogen to a selective catalystunder specifically selected process conditions.

The hydrocarbon feed used in the process of the present inventioncomprises polyaromatics. The term “hydrocarbon feed” as used hereinrelates to the hydrocarbon mixture that is subjected to the process ofthe present invention. Preferably, the hydrocarbon feed used in theprocess of the present invention comprises at least 10 wt-%polyaromatics, more preferably at least 20 wt-% polyaromatics and mostpreferably at least 30 wt-% polyaromatics. Preferably, the hydrocarbonfeed used in the process of the present invention is selected from thegroup consisting of heavy cycle oil, light cycle oil, carbon black oil,cracked distillate and pyoil.

The specifically selected process conditions used in the process of thepresent invention comprise a pressure of ambient-65 bara, a temperatureof 350-500° C., a WHSV of 0.1-10 h⁻¹ and a “hydrogen to hydrocarbon”ratio (H₂/HC ratio) of 1-20.

Preferably, the process conditions comprise a pressure of 10-40 bara.

Preferably, the process conditions further comprise a temperature oftemperature of 400-470° C., a WHSV of 1-3 h⁻¹ and a H₂/HC ratio of 3-10.

The selective catalyst used in the process of the present invention isdescribed herein as M/zeolite catalyst, wherein said M/zeolite catalystcomprises 0.05-2.5 wt-% of element M, wherein said element M is one ormore elements selected from Group 10 of the Periodic Table of Elements;and an aluminosilicate zeolite having a pore size of 6-8 Å and aSiO₂/Al₂O₃ ratio of 50-120.

Zeolites are well-known molecular sieves having a well-defined poresize. As used herein, the term “zeolite” or “aluminosilicate zeolite”relates to an aluminosilicate molecular sieve. An overview of theircharacteristics is for example provided by the chapter on MolecularSieves in Kirk-Othmer Encyclopedia of Chemical Technology, Volume 16, p811-853; in Atlas of Zeolite Framework Types, 5th edition, (Elsevier,2001). Preferably, the catalyst comprises a large pore sizealuminosilicate zeolite. Suitable zeolites include, but are not limitedto, zeolite Y, faujasite (FAU), beta zeolite (BEA) and chabazite (CHA).The term “large pore zeolite” is commonly used in the field of zeolitecatalysts. Accordingly, a large pore size zeolite is a zeolite having apore size of 6-8 Å.

The aluminosilicate zeolite used in the process of the present inventionhas a SiO₂/Al₂O₃ ratio of 50-120. Means and methods for quantifying theSiO₂ to Al₂O₃ molar ratio of a zeolite are well known in the art andinclude, but are not limited to AAS (Atomic Absorption Spectrometer) orICP (Inductively Coupled Plasma Spectrometry) analysis.

Preferably, the M/zeolite catalyst comprises an aluminosilicate zeolitehaving a SiO₂/Al₂O₃ ratio of 60-100. More preferably, the M/zeolitecatalyst comprises an aluminosilicate zeolite having a SiO₂/Al₂O₃ ratioof 70-90, even more preferably a SiO₂/Al₂O₃ ratio of 75-85 and mostpreferably a SiO₂/Al₂O₃ ratio of about 80.

Accordingly, element “M” as used herein is one or more elements selectedfrom Group 10 of the Periodic Table of Elements. Preferably, theM/zeolite catalyst comprises 0.5-2 wt-% of element M. All weightpercentages of element M as provided herein relate to the amount ofelement M in relation to the total catalyst composition. Preferably,element M is one or more elements selected from the group consisting ofPd and Pt. Most preferably, element M is Pt.

The catalyst composition as used in the process of the present inventionmay comprise further components such as a binder. Known binders include,but are not limited to silica, alumina and clay, such as kaolin. Alumina(Al₂O₃) is a preferred binder. The catalyst composition of the presentinvention preferably comprises at least 10 wt-%, most preferably atleast 20 wt-% binder and preferably comprises up to 40 wt-% binder.

The catalyst composition is preferably formed into shaped catalystparticles by any known technique, for instance by extrusion.

Preferably, the aluminosilicate zeolite has a 12-ring structure. Thesespecific aluminosilicate zeolites are well known to the skilled man. Anoverview of their characteristics is for example provided by the Atlasof Zeolite Framework Types, 5th edition, (Elsevier, 2001). Accordingly,an aluminosilicate zeolite having a 12-ring structure is analuminosilicate zeolite wherein the pore is formed by a ring consistingof 12 [SiO₄] or [AlO₄]⁺ tetrahedra.

Preferably, the aluminosilicate zeolite is zeolite Y. Depending on thesilica-to-alumina molar ratio (“SiO₂/Al₂O₃ molar ratio” or “SiO₂/Al₂O₃ratio”) of their framework, synthetic faujasite zeolites are dividedinto zeolite X and zeolite Y. In X zeolites the SiO₂/Al₂O₃ ratio isbetween 2 and 3, while in Y zeolites it is 3 or higher. Accordingly,zeolite Y is a synthetic faujasite zeolite having a SiO₂/Al₂O₃ ratio intheir framework of 3 or more. Preferably, the zeolite in the selectivealkylation catalyst is in the so-called hydrogen form, meaning that itssodium or potassium content is very low, preferably below 0.1, 0.05,0.02 or 0.01 wt-%; more preferably presence of sodium is below detectionlimits.

Preferably, the zeolite y is partially dealuminated. Preferably, thezeolite Y used in the process of the present invention has a SiO₂/Al₂O₃ratio of 60-100. More preferably, the zeolite Y used in the process ofthe present invention has a SiO₂/Al₂O₃ ratio of 70-90. Preferably, thepartially dealuminated zeolite is prepared by controlling SiO₂/Al₂O₃ratio during zeolite synthesis. Alternatively, the zeolite may bepartially dealuminated by a post-synthesis modification. Means andmethods to obtain dealuminated zeolite by post-synthesis modificationare well known in the art and include, but are not limited to the acidleaching technique; see e.g. Post-synthesis Modification I; MolecularSieves, Volume 3; Eds. H. G. Karge, J. Weitkamp; Year (2002); Pages204-255. The aluminosilicate zeolite may comprise super cages having asize of 12-14 Å. Means and methods for preparing zeolites comprisingsuper cages are well-known in the art and comprise zeolitepost-treatments such as acid leaching and steaming, among others.(Angew. Chem., Int. Ed. 2010, 49, 10074, ACS nano, 4 (2013) 3698).

The process of the present invention produces monoaromatic hydrocarbonsas a process product. Preferably, the process of the present inventionproduces at least 20 wt-% monoaromatic hydrocarbons of the totalhydrocarbon process product, more preferably at least 25 wt-%monoaromatic hydrocarbons of the total hydrocarbon process product, andmost preferably at least 30 wt-% monoaromatic hydrocarbons of the totalhydrocarbon process product. Preferably, the process of the presentinvention produces less than 1.5 wt-% methane of the total hydrocarbonprocess product, more preferably less than 1 wt-% methane of the totalhydrocarbon process product and most preferably less than 0.5 wt-%methane of the total hydrocarbon process product.

It is noted that the invention relates to all possible combinations offeatures described herein, particularly features recited in the claims.

It is further noted that the term “comprising” does not exclude thepresence of other elements. However, it is also to be understood that adescription on a product comprising certain components also discloses aproduct consisting of these components. Similarly, it is also to beunderstood that a description on a process comprising certain steps alsodiscloses a process consisting of these steps.

EXAMPLE

Catalyst Preparation

Physical Mixture Catalyst:

The physical mixtures of hydrogenation and solid acid catalysts arecomposed of commercially available catalyst samples. The hydrogenationcatalyst is a Pt/Al₂O₃ from UOP, namely R-12. The zeolite is anunmodified zeolite Y from Zeolyst, namely CBV 780. These samples havebeen mixed in a 1 to 1 weight ratio.

Bifunctional Pt/Zeolite Y Catalyst:

65 grams of Zeolyst CBV 780 are divided into 3 ceramic dishes andcalcined in air at 100° C. for 3 hours to 300° C. and then to 550° C.for 10 hours using a ramp rate of 3° C./min.

After calcination, 15 grams of pre-dried sample are dispersed in 1 literof deionized water and stirred at 65° C. overnight. The next day thetemperature is raised to 70° C. and a solution of 0.317 g of Pt(NH₃)₄(NO₄)₂ is dissolved in 76.4 g of DI-H20 and added drop wise over aperiod of 7 hours. The material is allowed to stir overnight at 70° C.prior to filtering off the liquid. The filter cake is re-suspended in 1liter of fresh DI-H20 and allowed to stir for 15 min and subsequentlyfiltered again. The washing step is repeated twice more. The material isthen allowed to dry overnight on filter paper at room temperature. Next,the material is dried at 80° C. for 3 hours, pressed (10,000 psi),crushed and sieved (35-60 mesh sizing scheme). The sized material isloaded in a tube furnace with an air flow rate of 2.2 L/min. The furnaceis heated to 100° C. for 3 hours then to 300° C. for 3 hours at a ramprate of 0.2° C./min. Subsequently, the material is further calcined to350° C. at 0.2° C./min for 3 hours. The flows rates are then turned downto down to 1 L/min for 1 hour then to 345 ml/min for 1 hour while 350°C. is maintained. The material is then transferred to the calcinationoven and calcined for 3 hours in air using the same ramp rate of 0.2°C./min.

Experimental Set-Up

The experimental program was conducted on a fully automated 16-foldtrickle-flow hydro process unit allowing uninterrupted catalyst testing.The operating range of this unit is summarized in Table.

The 16-fold trickle-flow hydro processing unit operates as follows: Thefeed is preheated and mixed with hydrogen prior to entering theevaporation zone located on the top part of the set-up. Therein themixture is heated to the selected reaction conditions. The pressure inthe reaction section is maintained with a nitrogen pressure hold gassystem (PHG) at the reactor outlet. The reactor section is composed of a5 mm internal diameter tube with an isothermal zone of 50 mm at thehighest operating temperature. Once the reaction has taken place theeffluent is sent to a condenser kept at 75° C. Therein the gas isseparated from the liquid and sent to an online GC (every 90 min). Theliquid collected during reaction is stored and subsequently analyzedoffline in a GC-MS. Both, the gas and liquid flows are preciselymeasured to obtain the combined effluent composition.

TABLE 1 16-fold trickle-flow hydro processing unit specifications.Set-up specifications Temperature up to 500° C. Pressure up to 100 baraOperation mode Trickle-bed Catalysts volume up to 1.92 ml Reactor innerdiameter 5 mm Gases H₂, N₂, Ar

Model Feed Composition

The experiments have been carried out with a synthetic feed composed ofparaffin's (25 wt %), mono-aromatics (20 wt %), di-aromatics (55 wt %)and tri-aromatics (5 wt %). This is summarized in table 2.

TABLE 2 Model feed composition details. Model Feed Decane 25 wt %Propylbenzene 20 wt % Naphthalene 25 wt % 1-Methylnaphthalene 10 wt %2-Methylnaphthalene 15 wt % Anthracene  2 wt % Phenantrene  3 wt %

Catalyst Preparation and Reactor Loading:

The series of catalysts tested displayed different sizes and shapes. Tominimize the influence of external mass transfer limitations and comparethe intrinsic reactivity of each catalyst, similar sieved fractions wereused. To this end, zeolite powders were bound with alumina sol, dried,calcined and sieved to the desired size. The zeolite containing samples(namely, solid acid catalysts and/or bifunctional catalysts) were mixedin a 7 to 3 ratio with Dispersal® and the resulting mixture mixed withwater (1 to 5 ratio). Subsequently, the slurry was milled (5 min, 600rpm), dried in a hot box (110° C., overnight), calcined in air (300° C.,6 h) and sieved to a target fraction of 125-160 μm. On the other hand,the hydrogenation catalysts were milled and sieved to the same targetfraction as the zeolite containing samples.

The catalysts were loaded in the reactors together with silicon carbidediluent to form a bed which is ring shaped around a thermowell. Athorough calibration was performed to determine the isothermal zone ofthe 16 parallel reactor set-up under the temperature conditions tested.

Activation Protocol

The activation and soaking protocol details are summarized in Table 3.After loading the catalyst in the reactor the activation procedure isperformed to reduce the metal particles contained in the catalyst.Subsequently, the hydrogen feed is replaced by a mixture of hydrogen andthe hydrocarbon feed used in the experiments while the sample is heatedup slowly to reaction conditions. This is the so-called soakingprocedure.

TABLE 3 Activation and soaking protocol details. Activation procedureSoaking procedure Temperature 60-400° C. Temperature 60° C. Heating ramp1° C./min, WHSV 2 h⁻¹ 2 h hold at 400° C. Purge step N₂ during 10 minPurge step N2 during 10 min Reduction H₂ H₂ flow 10 (I/h) step H2 flow41.5 (I/h) Pressure 30 bara Pressure 30 bara Duration 16 h Duration 460min + Cool down

Experimental Results

The physical mixture catalyst and bifunctional Pt/Zeolite Y catalyst,all prepared as described herein above, were contacted with the modelfeed using the following reaction conditions: a WHSV of 1 h⁻¹, a H₂:HCratio of 10, a pressure of 30 bara and a temperature of 400 or 450° C.The process was performed in a continuous system that operated in steadystate conditions. In Table 4 the experimental results are describes asan average result of a measuring period of 24 h. Data were generatedusing GC-MS as described herein above.

TABLE 4 Experimental results Mono- Temperature aromatics catalyst (° C.)(wt %) Pt/Zeolite Y 400 26.8 Physical 400 21.7 mixture Pt/Zeolite Y 45033.6 Physical 450 28 mixture

1. A process for producing monoaromatic hydrocarbons from a hydrocarbonfeed comprising polyaromatics, the process comprising: contacting thefeed in the presence of hydrogen with a M/zeolite catalyst at a pressureof ambient-65 bara, a temperature of 350-500° C., a WHSV of 0.1-10 h⁻¹and a H₂/HC ratio of 1-20, wherein said M/zeolite catalyst comprises0.05-2.5 wt-% of element M, wherein said element M is one or moreelements selected from Group 10 of the Periodic Table of Elements; andan aluminosilicate zeolite having a pore size of 6-8 Å and a SiO₂/Al₂O₃ratio of 50-120.
 2. The process according to claim 1, wherein theprocess conditions comprise a pressure of 10-40 bara.
 3. The processaccording to claim 2, wherein the process conditions further comprise atemperature of 400-470° C., a WHSV of 1-3 h⁻¹ and a H₂/HC ratio of 3-10.4. The process according to claim 1, wherein the M/zeolite catalystcomprises an aluminosilicate zeolite having a SiO₂/Al₂O₃ ratio of60-100.
 5. The process according to claim 1, wherein the M/zeolitecatalyst comprises 0.5-2 wt-% of element M.
 6. The process according toclaim 1, wherein element M is one or more elements selected from thegroup consisting of Pd and Pt.
 7. The process according to claim 1,wherein the aluminosilicate zeolite has a 12-ring structure.
 8. Theprocess according to claim 1, wherein the aluminosilicate zeolitecomprises super cages having a size of 12-14 Å.
 9. The process accordingto claim 8, wherein the aluminosilicate zeolite is zeolite Y.
 10. Theprocess according to claim 9, wherein the zeolite Y is partiallydealuminated.
 11. The process according to claim 1, wherein thehydrocarbon feed is selected from the group consisting of heavy cycleoil, light cycle oil, carbon black oil, cracked distillate and pyoil.